Electric power steering control system

Abstract

In an electric power steering control system, a phase compensator of the steering torque is made of an analog circuit and an anti-phase compensator is made by the software of a microcomputer, thereby to eliminate the changes in the gain and the phase by the phase compensator of the analog circuit near the oscillation frequency, so that the steering torque signal equivalent to that of no phase compensation necessary for the computation at the observer is computed from the phase-compensated steering torque signal.

1. An electric power steering control system, comprising:
 a torque detection means that detects a steering torque caused by a driver; 
 a torque controller that computes an auxiliary torque current, which assists the steering torque, using the output of the torque detection means; 
 a motor that generates a torque which assists the steering torque; 
 a current detection means that detects a current value to be conducted to the motor; 
 a rotating speed estimation means that estimates the rotating speed of the motor; and 
 a damping controller that computes a damping current, which is added to the auxiliary torque current, using the estimate value of the rotating speed of the motor estimated by the rotating speed estimation means, wherein: 
 the rotating speed estimation means includes: a motor current steering component removal means that removes a component caused by steering from the output of the current detection means; a torque steering component removal means that removes a component caused by steering from the output of the torque detection means; and a rotating speed observer that computes the estimate value of the rotating speed of the motor using the current which has the steering component thereof removed by the motor current steering component removal means, and the steering torque outputted from the torque steering component removal means; and 
 at least one of a motor current phase lead reducer that diminishes a phase lead caused by the motor current steering component removal means, and a torque phase lead reducer that diminishes a phase lead caused by the torque steering component removal means is included. 
 
     
     
       2. The electric power steering control system according to  claim 1 , comprising an analog phase compensator, a torque signal converter, and a torque opposite phase compensator. 
     
     
       3. The electric power steering control system according to  claim 1 , wherein the current phase lead reducer and torque phase lead reducer are formed with low-pass filters. 
     
     
       4. The electric power steering control system according to  claim 3 , wherein
 the current phase lead reducer has a low-pass filter characteristic causing the ratio between a steering wheel oscillation frequency and the cutoff frequency of the current steering component removal means, and the ratio between the cutoff frequency of the current phase lead reducer and the steering wheel oscillation frequency, to be identical to each other; and 
 the torque phase lead reducer has a low-pass filter characteristic causing the ratio between the steering wheel oscillation frequency and the cutoff frequency of the torque steering component removal means, and the ratio between the cutoff frequency of the torque phase lead reducer and the steering wheel oscillation frequency, to be identical to each other.